The lactoperoxidase system (LPS) is a well known antimicrobial system and is composed of lactoperoxidase, thiocyanate and hydrogen peroxide. The system occurs naturally in milk. Although the mechanism of action is not completely understood, it is postulated that the system catalyses the oxidation of thiocyanate to hypothiocyanate and that the active antimicrobial is hypothiocyanate. Although LPS is known to affect gram negative organisms such as Salmonella, the effect has been shown to require 3 to 4 hours of contact. European Patent Application, Publication No. 0 252 051, assigned to EWOS Aktieboieg, discloses that the addition of an acid to adjust the pH of the lactoperoxidase enzyme in the dry state to between 3 and 5 increases the storage stability of the enzyme.
In PCT application, International Publication No. WO 88/02600, Poulsen discloses a bacteriocidal composition composed of lysozyme, peroxidase, a hydrogen peroxide forming enzyme and thiocyanate used for dental and wound treatment preparations. Lactoperoxidase is preferred. The composition was tested against Streptococcus, Lactobacillus, Bacteroides, Flavobacterium and Fusobacterium; all gram positive bacteria. Bacterial growth was reported to cease upon addition of the composition.
Nisin is the best known polypeptide of the lantibiotic group and is a well known, food acceptable, antimicrobial. However, although nisin is widely known to have an inhibitory effect on grampositive bacteria. It is generally believed to have no inhibitory effect on gram-negative bacteria. U.S. Pat. Nos. 4,597,972 and 4,584,199, assigned to Aplin and Barrett, disclose the use of 2000 to 10,000 International Units of nisin to prevent the outgrowth of spores of Clostridium botulinum in processed foods and food products.
Antimicrobial compositions which include synergistic amounts of two or more antimicrobials have been reported previously. PCT application, International Publication No. WO 89/12399, assigned to the Public Health Research Institute of the City of New York, discloses combinations of lantibiotics, such as nisin, and a chelating agent provide enhanced activity and a broader spectrum of activity on both gram negative and gram positive organisms.
Synergistic combinations of lysozyme and cecropins or sarcotoxin have been reported to lyse or inhibit eucaryotic cells in PCT application, International Publication No. WO 89/00194, assigned to the Louisiana State University Agricultural and Mechanical College. The disclosure states that the activity of a lytic polypeptide such as a cecropin or sarcotoxin may be enhanced by combination with lysozyme. Such synergistic combinations may be used not only to lyse or inhibit eucaryotes, but also bacteria, and that use applications suggested include use in food stuffs and other products as an antibacterial preservative and in agricultural application, for example, in a spray applied in an effective amount to crops to prevent infection by, or to inhibit plant pathogens.
Previous work commonly assigned herein, has found that nisin and lysozyme provide a synergistic antimicrobial combination against bacteria, particularly Listeria.
There have been no reports to date on the activity of a combination of the two antimicrobial systems, lactoperoxidase and nisin.
The synergistic antimicrobial composition of this invention has been found to be an effective cidal agent against the gram-negative organisms, such as Salmonella, in a much shorter time period than the lactoperoxidase system alone. As such it will be useful to eliminate surface contaminations of food products and as a disinfectant for food processing plants.